Hi everyone,
I am working with an mega128 and wish use the ADC in ADC noise reduction mode. So I set up the ADC and write the appropriate bits to the MCUCR register and...nothing happens. I am almost certain, at least, that the ADC conversion never starts.

If have looked through previous posts and although others have had similar problems, I have not been able to find a solution.

I have stripped down my program to the code below. It basically turns on two LEDs at the start and if a conversion complete flag is set, one of the LED turns off. Note that if I start the conversion the normal way: ADCSRA |=(1<<ADSC); then the ADIF is set and the LED does switch off.

What have I missed? How do I make the the ADC noide reduction mode switch off the CPU, start the ADC and wake up again?